The paper constitutes a description of the evolution of the system of presumptions pertaining to institution of parentage in Polish family law in the years 1946–1965. The following three legal acts were analysed: Family Law of 1946, constituting the first attempt at unification of regulations connected with this matter since 1918, when Poland regained independence, Family Code of 1950, abolishing the division into legitimate and illegitimate children, and the Family and Guardianship Code of 1964, with its legal regulations still in force (with subsequent amendments). The innovative analysis encompasses such problems as: division into legitimate and illegitimate children and its consequences, presumption of paternity, establishment of paternity in court, as well as legitimisation, recognition, and equalisation of a child. The changing situation of the legal entities connected with the institution of parentage, i.e. child, mother, father, and mother’s husband is also discussed in the article.